The usual practice in processing of silver halide color photographic materials is that used processing solutions are thrown away, generally as overflow solution.
However, these used processing solutions, which are recovered and treated as waste liquid, represent a high environmental pollution burden and are undesirable in terms of protection of the environment. Moreover, the cost of collection and shipment for the purpose of recovery cannot be ignored.
With regard to color development stages for color photographic material in particular, since the solutions concerned are highly alkaline and constitute a considerable organic pollution load as represented by the BOD (biochemical oxygen demand) and the waste liquid represents a large pollution load and since the chemicals are costly, various methods for reducing the amount of waste liquid have been proposed in the past.
For example, low-replenishment processing methods in which compositions of replenishment solutions for color development solutions (referred to below as `color development replenishment solutions`) are adjusted and the amounts of replenishment are reduced are disclosed in JP-A-61-251852 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-61-261741, JP-A-61-282841 and JP-A-61-70552, etc. A procedure one may cite for adjustment of the replenishment solution composition in low-replenishment processing is, e.g., to effect enrichment of consumed components such as the color developer and preservatives, etc. in the replenishment solution so that the necessary amounts of components are supplied even though the amount of replenishment is reduced. When a silver halide color photographic material is processed, halogen ions are released in the color development solution. In low-replenishment processing there is, in particular, an increase in the bromine ion concentration in the color development solution and this results in development inhibition. Therefore, the general practice to prevent this is to take measures to produce the bromide concentration in the replenishment solution so that it is less than it is in an ordinary replenishment processing. However, there is a certain limit even to this, and accumulation of bromine ions causes a slow-down of the progress of development. Further, a delicate variation in the bromine ion concentration causes changes in photographic characteristics, this trend being very marked in processing of a photographic material which has a silver iodobromide emulsion as a main component.
Another procedure that has been considered as a means for reducing waste liquid is the re-use of used processing solution (overflow solution) as replenishment solution. If re-use were possible, it would resolve the above-noted problems relating to waste liquid treatment. Also, since it would make it possible to re-use effective components remaining in the overflow solution, the amount of chemicals used would be less than in the case where replenishment solution is freshly produced. Thus, it would be possible to aim for further reduction of costs. Much research is therefore being conducted on so-called regeneration technology by which, as a regeneration means to make possible the re-use of used processing solution, fluctuations that occur during processing are corrected. The procedure employed generally is to remove accumulated components that have adverse effects on photographic performance while at the same time to add supplementary amounts of components that have been consumed and to use the solution again as a replenishment solution.
A particular problem in the past in regeneration technology has been the question of how to effectively remove accumulated components, and a particularly serious problem in color development stages has been the removal of bromine ions which are dissolved out from photographic material and have a strong development inhibition action.
Halogen removal methods using ion exchange resins have been proposed in, e.g., SMPTE J., 88, 168-171 (1979), JP-A-55-144240 and JP-A-53-132343. However, these methods require large equipment such as a resin column, etc., technology for halogen ion control is needed and batch processing can only be accomplished. Also, regeneration of the resin results in production of large amounts of waste liquid which gives rise to new treatment problems.
JP-B-61-52459 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-A-51-97432, etc. disclose halogen removal methods employing ion exchange membrane electrodialysis and JP-A-54-37731 (corresponding to U.S. Pat. No. 4,207,157) and JP-A-56-27142, etc. disclose continuous processing methods in which dialysis and removal are effected in a manner so that the concentrations of halogen ions and particularly of bromine ions in a development solution are kept constant by connecting the development solution tank and an ion exchange membrane electrodialysis tank, detecting and determining the quantity of bromine ions in the development solution and using these data to control the amount of current passed through the electrodialysis tank. A supplementary addition of processing agent components is made to the resulting overflow solution and thus solution is then used again as a replenishment solution. U.S. Pat. No. 4,207,157 discloses to continuously process a silver halide photographic material employing ion exchange membrane electrodialysis while conducting removal of a halogen. However, it does not teach how to stabilize sensitivity and gradation.
Since ion exchange membrane electrodialysis makes continuous operations possible and also makes halogen ion adjustment possible, it has the advantages that handling is easier than in ion exchange resin methods and that only a small amount of equipment space is needed. However, continuous processing using this ion exchange membrane electrodialysis procedure has been associated with the problem that when the halogen ion concentration is controlled to be constant, slight variation in the halogen ion concentration occurs because of variation in the current density, variation in the precision of halogen detection and variation in the concentration of the development solution due to condensation, etc. Thus, fluctuation in the photographic performance achieved (especially sensitivity and gradation) can easily occur, particularly in processing of a silver halide color photographic material.